JPH0680085B2 - Polymerization inhibitor composition and polymerization inhibition law - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polymerization inhibitor composition and a method for inhibiting polymerization of vinyl aromatic compounds that are easily polymerized.

It is well known that vinyl aromatic compounds such as monomeric styrenes, lower alkylated styrenes such as α-methylstyrene, readily polymerize, and further that the rate of polymerization increases with increasing temperature. Since vinyl aromatic compounds produced by ordinary industrial methods contain impurities,
In order to make these compounds suitable for many types of industrial applications, they must be subjected to separation and purification steps. Such separation and purification is generally accomplished by distillation.

Many known polymerization inhibitors have been used under normal refrigeration conditions to prevent polymerization of vinyl aromatic compounds during storage. For example, a common inhibitor useful in inhibiting the polymerization of vinyl aromatic compounds during storage conditions is 4-tert-
Includes butylcatechol (TBC) and hydroquinone.

On the other hand, sulfur has been widely used as a polymerization inhibitor in the distillation of various vinyl aromatic compounds. However,
Sulfur provides a reasonably effective inhibitor, but its use in such a distillation process brings about very serious drawbacks. The production of valuable waste material that is highly polluted with sulfur at the bottom of the reoiler of the distillation column. This waste material also causes serious problems of pollution and / or decontamination.

While many compounds are effective in inhibiting the polymerization of vinyl aromatic compounds under different conditions such as storage, some of these compounds are effective in inhibiting the polymerization of vinyl aromatic compounds under distillation conditions. I just know it is useful. A compound known to be effective in polymerization is 2,6-dinitro-p-cresol (DNPC) disclosed in Watson, US Pat. No. 4,105,506.
Furthermore, it has been discovered that the combination of conventionally known polymerization inhibitors can achieve greater inhibitory effects than either inhibitor alone. The synergistic effect of combining two known inhibitors is disclosed in Watson, US Pat. No. 4,061,545, in which phenothiazine and tert-butylcatechol (TBC) are used together as polymerization inhibitors in the presence of oxygen. . N-nitrosodiphenylamine and DN for inhibiting the polymerization of vinyltoluene under vacuum conditions
The synergistic effect of the combination of PCs is US Pat.
No. 341,600. However, it has been discovered that as the distillation temperature increases, the effectiveness of these inhibitors decreases.

In the distillation of vinyl aromatic compounds, high distillation temperatures are preferred to increase throughput and improve the energy efficiency of the distillation. However, these high temperatures increase the rate of polymerization and produce unacceptable amounts of polymer in the polymerization equipment. Therefore, there is a strong need for a polymerization inhibitor that effectively prevents the polymerization of vinyl aromatics during distillation at high temperatures.

Therefore, it is an object of the present invention to provide a composition for inhibiting the polymerization of vinyl aromatic compounds and a method for inhibiting the polymerization.

Another object of the present invention is to inhibit the polymerization of vinyl aromatic compounds and their polymerization at high temperature to obtain highly pure unsaturated vinyl aromatic compounds with high recovery and to produce less undesired by-products. It is to provide a method that does not discriminate.

A further object of the invention is a process for inhibiting the polymerization of vinylaromatic compounds which allows the operation of the compositions and the distillation apparatus at elevated temperatures and an increase in the processing rate without loss of efficiency. To provide.

With respect to achieving the above and other objectives, the present invention provides a composition for inhibiting a readily polymerizable vinyl aromatic compound in the presence of oxygen when subjected to elevated temperatures, such as in distillation. That is, an effective amount of 2,6-dinitro-p-cresol and an effective amount of the formula A composition comprising a phenylenediamine of the formula where R ₁ and R ₂ are alkyl, aryl or hydrogen is provided.

Vinyl aromatic compounds included in the present invention include styrene, substituted styrenes, divinylbenzene, vinyltoluene, vinylnaphthalene, and polyvinylbenzene. It is to be understood that this group also includes all its structural isomers.

Further in accordance with the present invention, a vinyl aromatic compound is added in an effective amount of 2,
A method of inhibiting the polymerization of a readily polymerizable vinyl aromatic compound comprising subjecting it to heating conditions such as distillation in the presence of 6-dinitro-p-cresol and the above mentioned phenylenediamine derivatives and oxygen. Provided.

According to the present method, the degree of polymerization occurring in the distillation apparatus at a high temperature of about 150 ° C. is considerably reduced as compared with the conventional method.
Furthermore, the distillation apparatus can be operated at higher temperatures and pressures than with conventional inhibitors, thus resulting in faster distillation rates.

Further objects, features and advantages of the invention will be apparent from the claims and the following detailed description.

FIG. 1 is a schematic diagram of one embodiment of the process of the present invention using a three column distillation train, and FIG. 2 utilizes direct injection of vinyl aromatic feed to the recycle column. It is a systematic diagram of another example of the method of this invention.

The present invention refers to 2,6-dinitro-p, hereinafter referred to as DNPC.
-Cresol and phenylenediamine derivatives are used as polymerization co-inhibitor composition during heating of vinyl aromatic compounds in the presence of oxygen.

The phenylenediamine of the present invention has the formula [In the formula, R ₁ is an alkyl group, an aryl group or hydrogen,
And R ₂ is an alkyl group, an aryl group or hydrogen]. The alkyl groups of R ₁ and R ₂ each have 1 to carbon atoms.
It is preferable to have 12. Examples of such suitable phenylenediamine derivatives are p-phenylenediamine, N,
N'-dimethylphenylenediamine, N, N'-diethylphenylenediamine, N, N'-bis (1,4-dimethylpentyl) -p-phenylenediamine, and N-4-methyl-
Includes 2-pentyl-N'-phenyl-p-phenylenediamine.

N, N'-bis (1,4-dimethylpentyl) -p-phenylenediamine and N-4-methyl-2-pentyl-N'-
It should be noted that phenyl-p-phenylenediamine is particularly suitable. However, N, N′−
Most preferred is bis (1,4-dimethylpentyl) -p-phenylenediamine.

The distillation technique of the present invention is suitable for use in separating readily polymerizable vinyl aromatic compounds from a mixture by virtually any type of method in which the compounds are subjected to temperatures above room temperature. Is. The term "polymerization inhibitor" used herein means to prevent undesired polymerization of a vinyl aromatic monomer at an elevated temperature such as in a distillation apparatus. Although there is an advantage that the distillation rate is increased by increasing the temperature of the distillation apparatus, this temperature increase also accelerates the polymerization rate. However, this rate is offset by the introduction of the inhibitors of this invention. In its most useful application, the composition is a distillation mixture of vinyl aromatic compounds selected from the group consisting of styrene, substituted styrenes such as α-methylstyrene, divinylbenzene, vinyltoluene, vinylnaphthalene, and polyvinylbenzene. Applied. The group is understood to include all structural isomers of the compounds mentioned above. A preferred application of the present invention is the distillation of crude styrene.

The amount of polymerization inhibitor added can be varied over a wide range depending on the distillation conditions. Generally, the degree of stabilization is proportional to the amount of inhibitor added. In accordance with the present invention, based on the vinyl aromatic feed to the BT column 10 or recycle column 90, a phenylenediamine concentration of about 50-2000 ppm and a DNPC concentration of about 100-2000 ppm are predominantly of the distillation mixture. It was found to give reasonable results depending on the temperature and the degree of prohibition expected. But preferably,
The phenylenediamine inhibitors of the present invention are about 50 to about 1000 ppm.
The concentration of DNPC is about 250 to about 1000ppm.
Is. The preferred ppm ratio of phenylenediamine to DNPC is 2: 3. There is no particular order in which the compounds of the invention may be combined. In one particular embodiment, it is added together outside the distillation train at ambient temperature and pressure and then injected there. The distillation technique of the present invention is suitable for reuse in separating readily polymerisable aromatic compounds from a mixture by virtually any method of subjecting the vinyl aromatic compound to a temperature above room temperature. is there.

Oxygen must be added to the system for the phenylenediamine co-inhibitor to work properly. For high concentrations of oxygen in the required areas, oxygen is added separately to the system. The oxygen used in the present invention may be in the form of oxygen or an oxygen-containing gas. If an oxygenated gas is used, the remaining components of the gas must be inert to the vinyl aromatic compound under distillation conditions. The most useful and most expensive oxygen source is air, which is suitable for the present invention. The amount of oxygen can vary widely, but it is generally desirable to use the amount found in air.

Referring to the drawings, FIG. 1 shows a benzene-toluene fractionating column 10, ethylbenzene or recycle column 12, and styrene or finishing column (fini), which are referred to in the industry as BT columns.
A typical styrene distillation train comprising a shing column) 14 is illustrated. It should be noted that the operating theory of this distillation method is very suitable for use with other modifications of other distillation equipment used for the purification of other vinyl aromatic compounds. As shown in FIG. 1, a crude styrene feed is introduced through feed conduit 16 into the central portion of BT column 10. BT Tower 10
May be of any suitable design known to those skilled in the art and may include any suitable number of vapor-liquid contacting means such as bubble trays, perforated trays and the like. However, column 10 typically contains less than 40 distillation trays. The tower 10 is equipped with a suitable reboiler 18 for applying heat thereto. The temperature of the reboiler 18 is generally about 190 to about 250 ° F.

Most of the polymer is produced in ethylbenzene or the recycle column 12, but a small but significant amount of all polymer produced during distillation is produced in the BT column 10. Therefore, a polymer inhibitor is needed in this column. In order to prevent polymerization in the BT tower 10, hereinafter referred to as DNPC 2,6
The -dinitro-p-cresol can be introduced separately into the BT column 10 via conduit 20 or into the crude styrene feed flowing in conduit 16. To facilitate the process, a phenylenediamine inhibitor may also be introduced into BT column 10 via conduit 20 or in the crude styrene feed flowing in conduit 16. The phenylenediamine inhibitor has little or no inhibitory action in the BT column due to the lack of oxygen, but it can be piped together with the BT column bottoms.
When it moves from 24 to the recirculation tower 12, it acts as the main inhibitor there. When the DNPC and / or phenylenediamine polymerization inhibitors are added as separate streams to the BT column 10, they are preferably dissolved in a volatile aromatic hydrocarbon diluent such as ethylbenzene. The position of the inhibitor supply conduit 20 is
In order to achieve an inhibitor distribution that closely matches the distribution in the tower 10 of the readily polymerizable vinyl aromatic compound,
It will normally be in the middle of the BT tower 10.

The overhead stream comprising benzene and toluene is removed from conduit 22 under the distillation conditions imposed on column 10. These low boiling aromatic hydrocarbons are subsequently condensed and stored for subsequent use. The bottom product of the BT column comprising styrene, ethylbenzene, inhibitor and tar serves as a recycle or feed to the ethylbenzene column. The bottom product is introduced by conduit 24 and pump 36 into the middle portion of the ethylbenzene column. Recycle column 12 may be of any suitable design known to those skilled in the art and may include 40-100 trays. However, preferably, the recycle column is of parallele path design. Furthermore, the recycle column likewise preferably contains as many as 72 trays in order to achieve a suitable separation between boiling styrene and ethylbenzene. B
The -T bottoms are preferably introduced in the middle section of the recycle column 12.

In the ethylbenzene column, a phenylenediamine composition introduced in the middle of column 12 from conduit 28, with BT bottoms through conduit 30, or with DNPC through conduit 20 into the BT column. Provides some degree of inhibitor protection. Due to the protection by DNPC in the rest of the distillation train, it is only necessary to add air to the recycle column. A more effective polymerization inhibitor is needed in the recycle column 12 as it is exposed to high temperatures up to 150 ° C, which is desirable for energy efficient distillation. at least
By knowing a temperature of 118 ° C., preferably 130 ° C. or higher, low pressure steam can be recovered from the overhead condenser (not shown) of the recycle column 12.

Each oxygen is introduced into the reboiler 32 through an air purge conduit. Alternatively, oxygen may be introduced into the reboiler 32 from the bottom or boot 40 through conduit 42 if there is sufficient air pressure / volume to reach the reboiler through conduit 43. In order for phenylenediamine to be effective, sufficient oxygen must be introduced to occupy the vapor space of column 12. Oxygen is dispersed over column 12 where it acts with phenylenediamine and inhibits polymerization there. Complete dispersion in air tower 12 generally does not occur. The presence of DNPC there therefore acts as a co-inhibitor in the case where the effect of phenylenediamine is diminished due to the absence of air. Hence the DNPC
Continues to act as a polymerization inhibitor in the area of the recirculation column 12 in the absence of air, and as a result, phenylenediamine as a whole, as compared to when present alone or in combination with other oxygen activated inhibitors. Gives a high polymerization inhibition effect.

Surprisingly, it has been discovered that DNPC is not only compatible with phenylenediamine but also acts as a polymerization inhibitor in the presence and absence of oxygen. Therefore, DNPC effectively provides inhibitor protection in addition to the effect exhibited by phenylenediamine in the area of the recirculation tower where the air is dispersed.
However, it was discovered that NDPC was consumed more quickly when DNPC was used alone as an inhibitor in the presence of air. This is due to the fact that many polymer free radicals are formed in the presence of air. Therefore, it is necessary to add more DNPC inhibitor to maintain an effective DNPC / oxygen polymerization inhibition over a long period of time. Further DNPC and phenylenediamine protection can be obtained by returning the tar containing DNPC / phenylenediamine to the recycle column 12 as described in US Pat. No. 4,272,344.

In addition, the phenylenediamine inhibitor is BT from the conduit 20.
It can be introduced into the column as a DNPC / phenylenediamine mixture together with a DNPC inhibitor. There is no suitable order for mixing them together. Any mixing order at ambient temperature and pressure will give reasonable results. Part of DNPC / phenylenediamine passes through the BT tower and is recycled along with the BT bottom product.
Enter 12

The bottom portion of the recycle column 12 comprising the styrene inhibitor and tar is withdrawn from the reboiler zone of the recycle column 12 via conduit 60. The recycle column bottoms are then introduced by pump 62 from conduit 64 into the styrene or intermediate portion of finishing column 14. Optionally, bottoms material may be introduced through conduit 66 to the lower portion of styrene column 14.

Finishing tower 14 may be of any suitable design known to those of ordinary skill in the art. A typical column would contain, for example, about 24 distillation trays. The reoiler 68 has a conduit 78 at the bottom 76 of the tower.
And the pump 80. The reboiler 68 is typically operated at a temperature of about 82 to about 121 ° C. In general, inhibitor protection is present in the bottoms feed for this column.
Appropriately provided by DNPC and phenylenediamine. A portion of the tar from column 14 can be returned at least from conduit 88 to ethylbenzene column 12 to further replenish DNPC in the system.

The high purity styrene overhead product is withdrawn from styrene column 14 via conduit 74. The bottom product of the styrene column consisting of polystyrene, undistilled styrene, heavy by-products and DNPC / phenylenediamine co-inhibitor is removed from the reoiler recycle conduit 78 and flashed from conduit 85 for further processing. Send to a pot (flash pot). In the flush pot, residual styrene is removed from the styrene column bottoms and returned to the styrene column via conduit 86. Tar generated in flash pot 84 is continuously removed from the system via conduit 83 or a recirculation tower via conduit 88.
12 or return to BT tower 10.

FIG. 2 shows an example of application of the distillation method of the present invention to another typical distillation train. The styrene feed is introduced through conduit 91 to the middle section of recycle column 90, which is preferably a parallel distillation channel design. Conduit 92 supplies a phenylenediamine inhibitor to recycle column 90. Tower 90 by reboiler 94
Supply heat to the bottom of the tower. Oxygen to air purge conduits 96 and 98
Through reboiler 94. Oxygen is passed through the bottom or boot 100 and conduit 101 if there is sufficient oxygen pressure and capacity to reach the reboiler from conduit 97.
It may be directly introduced into 94. In BT column 122, benzene and toluene are withdrawn as overheads through conduit 123 and then condensed for further use. The ethylbenzene bottoms product is removed from conduit 124 and circulated for reuse. The reboiler 126 provides the BT column 122 with the heat required for distillation.

Conduit 12 the recycle column bottoms containing polystyrene, undistilled styrene, heavy by-products, phenylenediamine and DNPC.
Take out from the recirculation tower through 8. The impure styrene fraction is then pumped through the pump 132 and conduit 133 to the styrene column 130.
Supply to the upper part of. Sometimes impure styrene is conduit 134
It may be introduced into the lower region of the styrene column through. A reboiler circuit comprising a reboiler 136 and a pump 138 is attached to the styrene or finishing tower 130 to provide it with the necessary heat. DNPC is preferably introduced into the recycle column along with phenylenediamine through conduit 92. The purified styrene overhead product is removed via conduit 144.

The reboiler 148 is connected to the bottom 136 of the finishing tower through a recirculation conduit 145 and a pump 150. The bottoms product of the finishing tower is removed from reboiler recycle line 145 for further processing in flash pot 146. Flash pot 146 is returned to finishing tower 130 via conduit 149. Tar generated in the distillation process is taken out from the conduit 152 or returned to the distillation column through the conduit 154.

By using the composition and method of the present invention, it is possible to increase the temperature of the recirculation tower by introducing an effective amount of DNPC / phenylenediamine. It is possible to drive. In addition, DNPC inhibitors can be used in the remaining fractionation columns to ensure effective polymerization inhibition in the absence of air at low temperatures. Therefore, high distillation temperatures and high pressures can be utilized without producing undesired amounts of polymer. In this case, the distillation rate can be increased without increasing the degree of polymerization that has been experienced in conventional distillation processes.

In addition, by optimizing the distribution of DNPC / phenylenediamine inhibitors in the recirculation column and by optimizing the distribution of DNPC inhibitors in the remaining fractionation columns of the distillation train, Higher temperatures than in the distillation process can be achieved in the recycle column, allowing more effective energy recovery therefrom.

The following examples are presented in order to more fully describe the invention. However, this is an example of the present invention, and the present invention is not limited in any sense.

Example 1 Two 100 ml reaction flasks were prepared. One flask (1) was charged with 25 g of styrene, and DNPC was 100 ppm.
And Flexone 4L (trade name of Uniroyal Chemical; Flexone
4L has the chemical formula N, N′-bis (1,4-dimethylpentyl) as discussed in the Uniroyal Material Safety Sheet, which covers Flexone 4L, which is incorporated herein by reference.
50 ppm (with p-phenylenediamine) was added. The second flask (2) was charged with 25 g of styrene,
DNPC 200 ppm was added to this. These flasks were fitted with a magnetic stirrer and septum stopper and heated to 138 ° ± 2 ° C in a stirred oil bath. The first flask was bubbled with about 3 ml / min of air below the surface of the liquid during the distillation. Nitrogen was bubbled through the second flask. After 2 hours, the samples were tested for the extent of styrene polymerization by measuring the change in refractive index. In this test, the monomer was sometimes distilled off, and the remaining polymer was weighed. The final polymer yield was 14.94% in the first flask, while the final polymer yield was 18.24% in the second flask. It showed that the phenylenediamine / DNPC co-inhibitor system had a better inhibitory effect at high temperature than DNPC alone.

Example 2 A 12 ″ diameter pilot plant fractionator packed with Norton Intalox packing was used to remove ethylbenzene and styrene.
The 1: 1 mixture was distilled. The column could be continuously fed and withdrawn overhead to mimic a conventional recycle column. The tower has DNPC 300 ppm (based on styrene content) and Flexo
200 ppm ne 4L (based on styrene content) was introduced.
Air was introduced into the tower at a rate of 1.2 / min. The reboiler temperature was maintained at 118 ° C. The bottoms were removed every 30-60 minutes to maintain a constant reboiler level. The feed rate, column top velocity, column temperature distribution, reflux ratio and column top pressure were measured at time intervals. Bottom and top samples were collected at 2 hour intervals.
The aldehyde and peroxide contents in the overhead distillate were measured at 6-8 hour intervals. Also, a part of the bottom product is evaporated to dryness under vacuum, a part of the bottom product is placed in a flask, the flask is heated to drive off the monomer, and then the remaining amount of the polymer is weighed. Therefore, the percentage of polymer in the bottoms was determined.

The following results were obtained.

Weight body yield: 0-0.21% Aldehyde: 181-427ppm Peroxide: 13-25ppm For further testing, the rate of oxygen was 0.50-0.25, then
It was reduced to 0.10 / min. At this time, the polymer yield was in the range of 0.24 to 0.36%.

Example 3 DNPC 300ppm and Flexone 4L 200PPm (118 ° C of Example 2
Example 2 by using the same concentration as used in Example 2).
I followed the method. The temperature of the reoiler was maintained at 132 ° C.

The following results were obtained.

Polymer yield: 0.80 to 1.22% Aldehyde: 280 to 346 ppm Peroxide: 48 to 80 ppm As a further test, oxygen flow rate was 0.50 to 0.25, then
It was reduced to 0.10 / min. As a result, the polymer yield is
It increased slightly from 1.24 to 1.47%.

Comparative Example DNPC By using only 1000 ppm as an inhibitor,
The method of Example 2 was followed.

The following results were obtained.

Polymer yield: 2.70 to 3.00% Aldehyde: 220 to 260 ppm Peroxide: 49 to 96 ppm Although the present invention has been described in various preferred embodiments and illustrated in numerous examples, those skilled in the art will appreciate various modifications thereof. It will be understood that substitutions, omissions and changes cannot be made without departing from the spirit of the invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram of one embodiment of the process of the present invention using a three column distillation train, and FIG. 2 utilizes direct injection of vinyl aromatic feed to the recycle column. It is a systematic diagram of another example of the method of this invention.

Front Page Continuation (72) Inventor Debra El Kendall Texas, USA 79720 Bitspring Marshall Drive Number 5 801 (72) Inventor Karen A. Mickelson Texas, USA 79413 Rabosk Huy Futain Inn Street 3402

Claims (8)

[Claims] 1. A) 100-2000 ppm of 2,6-dinitro-p-
Cresol, and b) 50-2000 ppm formula A phenylenediamine of the formula where R ₁ and R ₂ are alkyl, aryl or hydrogen, and a composition for inhibiting the polymerization of vinyl aromatic compounds in the presence of oxygen. 2. The composition according to claim 1, wherein the vinyl aromatic compound is selected from the group consisting of styrene, substituted styrene, divinylbenzene, vinyltoluene, vinylnaphthalene and polyvinylbenzene, and structural isomers thereof. object. 3. A composition according to claim 1 wherein the alkyl group contains from 1 to 12 carbons. 4. When heating a vinyl aromatic compound in the presence of oxygen, 100-2000 ppm of 2,6-dinitro-p-cresol and a formula of 50-2000 ppm. A method of inhibiting the polymerization of vinyl aromatic compounds comprising adding phenylenediamine of the formula: wherein R ₁ and R ₂ are alkyl, aryl or hydrogen. 5. The method according to claim 4, wherein the vinyl aromatic compound is selected from the group consisting of styrene, substituted styrene, divinylbenzene, vinyltoluene, vinylnaphthalene and polyvinylbenzene, and structural isomers thereof. . 6. The method according to claim 4, wherein the alkyl group contains 1 to 12 carbon atoms. 7. A process according to claim 4 in which the vinyl aromatic compound is heated to a temperature of up to 150 ° C. 8. A method according to claim 4 wherein heating of the vinyl aromatic compound occurs during distillation of the compound.